In the past 10 to 15 years the use of extracorporeal hemodialyzers in the treatment of patients with chronic renal insufficiency has become very popular. Otherwise known as "artificial kidneys" these devices supply the necessary missing renal function. The lack of this renal function would otherwise result in death of these patients. Other uses of artificial kidneys have been found for short-term use where renal function has been temporarily retarded due to the trauma of surgery of where renal function is insufficient due to the large scale ingestion of toxic substances.
To maintain the consistency of the human internal environment, the human kidney performs several functions. It detoxifies certain organic compounds, it synthesizes both hormones and enzymes, it excretes waste, and it also maintains the balances for water, electrolytes, acids and bases. In performing these functions, the kidney regulates the concentration of most of the constituents of the plasma; these include urea, uric acid, creatine, phenols, water, and the ions of sodium, potassium, calcium, magnesium, bicarbonate, chloride, phosphate, and sulfate. The artificial kidney performs one of these major functions, the removal from the body of certain potentially toxic substances all of which are soluble in water and adjust the levels of the blood constituents.
The prior art discloses a number of artificial kidneys which can be broadly classified into the parallel-plate dialyzers and coil-type dialyzers. For a description of the parallel-plate dialyzers see Kiil, "Development of a Parallel-flow Artificial Kidney in Plastics" Acta Chir. Scand. Supplement 23: 142, 1960. The coil type dialyzers have inherent disadvantages which make them less appealing than the parallel plate dialyzers. For instance, due to the large pressure drop in the blood flow path of the coil type dialyzers, it is normally necessary to employ a blood pump. The use of blood pumps results in serious complications. For one thing, they cause damage to blood cells and, in the treatment of chronic illnesses, this blood cell damage can ultimately affect the health of the patient. Furthermore, a large volume of blood is required to prime these units. This usually necessitates a transfusion with each treatment with the attendant cost and danger of infection. Notwithstanding the serious deficiencies of the coil-type dialyzers, they have substantially displaced the parallel plate dialyzers. The reason for this is the relatively long period of time required by parallel plate dialyzers to effect the required dialysis. For instance, the coil type dialyzer requires approximately 18 hours of treatment per week for an adult patient, usually three six-hour treatments. On the other hand, the parallel plate dialyzer requires twice this treatment time, 36 hours per week. As a result, there are essentially no parallel plate dialyzers in use today in the United States.
Because of the inherent advantages of the parallel plate dialyzers as opposed to the coil type dialyzer, the applicants thought it desirable to improve the parallel plate dialyzer to eliminate its drawbacks. Elimination of these drawbacks would enable practical use of the parallel plate dialyzer in order to enjoy the inherent advantages of this type of apparatus.
In order to enable utilization of the parallel plate dialyzer, we sought to increase the rate of dialysis by modifying the conventional parallel plate dialyzer and at the same time retaining the inherent advantages of this apparatus. The major modification made to the conventional dialyzer was to provide for the use of two dialysate solutions, one hypertonic and one hypotonic with respect to the blood. This modification in the dialysis process required modification of the dialyzer apparatus. Furthermore, in place of the conventional dialysate solution, we employ a novel hypotonic solution and a novel hypertonic dialysate solution. Experimental evidence indicates that the dialyzing apparatus disclosed in this application increases the rate of dialysis over the conventional parallel plate dialyzer by approximately six times and indeed, the dialyzing apparatus of the present invention operates at a faster rate than does the conventional coil dialyzer. Thus, applicants have succeed in overcoming the major disadvantage of the parallel plate dialyzer; its low rate of dialysis to the point where the parallel plate dialyzer of the present invention is not only comparable to the coil dialyzer in dialysis rate, but is actually faster than the coil dialyzer as well.